This invention relates, in general, to bleaching agents, their manufacture and use in detergent compositions, and their application to laundry operations. More specifically, the invention relates to bleaching agents, and bleaching detergent compositions containing such agent, which provide effective low-temperature bleaching of fabrics while substantially avoiding dye damage to bleach-sensitive fabrics.
Peroxygen compounds, such as perborates and percarbonates, which form hydrogen peroxide in aqueous solution are commonly used in bleaching and washing compositions to promote the bleaching of soiled fabrics. Washing compositions of this type are particularly prevalent in Europe and other countries which use relatively high washing temperatures, often near the boiling point of water, for laundering in automatic washing machines. In the United States, on the other hand, the use of peroxygen compounds in washing and bleaching compositions has been relatively limited due to the fact that such compounds are not optimally effective at temperatures below 80.degree. C., the range of washing temperatures in the United States being generally from about 30.degree. C. to 60.degree. C. Moreover, even in Europe and those other countries where much higher washing temperatures are conventional, there is a trend towards washign at temperatures from about ambient to 60.degree. C. because of the increasing use of synthetic fibers in clothing manufacture, materials which do not readily tolerate elevated washing temperatures.
In an effort to provide enhanced bleaching activity at lower temperatures, bleach activators of different types have been employed in combination with the peroxygen compounds, the interaction of the activator and peroxygen compound forming a peroxyacid in the wash solution which is the active species for bleaching. Activators of this type are extensively described in the prior art.
Another approach has been to use pre-formed organic peroxyacids to effect bleaching in laundry wash solutions. Monoperoxyphthalic acid (also referred to herein as MPPA for convenience) and, in particular, its magnesium salt is described as an effective bleaching agent in European Patent Application No. 0,027,693, published Apr. 29, 1983. However, as a practical matter, the use of MPPA and/or its magnesium salt for low temperature bleaching has a significant disadvantage with regard to certain dyed fabrics which are particularly sensitive to such bleach and interact therewith in the wash solution. This type of interaction frequently results in dye-damaged fabrics, the resultant effect being commonly referred to as "pin point" bleaching or spotting. The phenomenon of "pin point" spotting is believed to be due, in part, to a localized high concentration of bleach at the fabric surface where it reacts with a dye which is especially sensitive to such bleach and forms a pattern of bleached "spots" in a portion of the fabric. Consequently, there is a need in the art for a bleaching agent which is particularly active at low washing temperatures, yet safe enough for use such that it substantially avoids fabric damage by pin point spotting.
In U.S. Pat. No. 3,847,830 there is disclosed a peroxygen containing composition comprised of a particulate "normally unstable" peroxygen or peroxyacid compound enveloped by a layer consisting of less than 15%, by weight, of a water insoluble agent. Among the recommended enveloping agents are fatty acids containing from 8 to 26 carbon atoms. The function of the layer enveloping the peroxygen or peroxyacid compound is to enhance the storage stability of such compounds by preventing their decomposition in a humid environment such as typically generated in a sealed container wherein a peroxygen or peroxyacid compound is in admixture with a particulate detergent composition.
U.S. Pat. Nos. 4,385,008 and 4,403,994 address themselves to the specific problems of storage stability and impact sensitivity of the magnesium salts of peroxycarboxylic acid compounds. The patents disclose the combination of magnesium monoperoxyphthalic, for example, with a desensitizing diluent selected from among broad classes of materials including hydrocarbon waxes, fatty acids, aromatic acids and esters, starch, cellulose and protein. With specific regard to the fatty acids, the patents state that "although any aliphatic acid can be used, for practical purposes, the acid normally contains from 10 to 26 carbon atoms . . . ". Lauric acid (a 12 carbon atoms acid) is said to be especially preferred for this purpose.
U.S. Pat. No. 4,655,780 to Chun et al addresses itself to the problem of pinhole bleach damage and describes chlorine bleaching particles encapsulated in a blend of fatty acid soaps of specified chain length. The effective soap blend is said to be a mixture of C.sub.12 -C.sub.14 fatty acid soap with C.sub.16 -C.sub.18 fatty acid soap. A binder is described as an "essential element" of the described bleaching composition. Lauric acid (a C.sub.12 acid) is said to be "the binder of choice."
Accordingly, while encapsulated chlorine bleach particles have been described in the art to overcome "pin point" spotting, and while the general combination of magnesium monoperoxyphthalate (MMPP) with a diluent or outer layer has been contemplated, the problem of "pin point" spotting of bleach-sensitive fabrics attendant to the use of MMPP for low temperature bleaching remains a problem yet to be addressed or solved.